Don your anorak and get technical about airplanes.
#907529 by abraxias
21 Jul 2015, 14:29
OK so the engines on a 747 have over 30,000lbs of thrust. How the hell are they attached by what looks like a very thin piece of metal to the wings and yet not get ripped off? This question has been bugging me for years. I'm sure the answer is that the engine's strut is actually capable of withstanding tens of thousands of pounds of thrust more but it just looks so flimsy!
#907530 by tontybear
21 Jul 2015, 14:38
there is actually a lot of structural integrity in the wing to be able to support the weight of the engines.

And remember the wings are also used a fuel tanks so even more weight.
#907543 by mallin
21 Jul 2015, 19:02
This is in reply to your question from my husband, an ex RAF aircraft engineer.

They are lifted into position using winches and fixed to the wing with great big bolts or pins. These pins are in some cases up to two inches in diameter.... They will not break.
#907547 by PilotWolf
21 Jul 2015, 20:03
mallin wrote:This is in reply to your question from my husband, an ex RAF aircraft engineer.

They are lifted into position using winches and fixed to the wing with great big bolts or pins. These pins are in some cases up to two inches in diameter.... They will not break.


Actually I think the bolts are the weak point designed to allow the engine to break away in certain circumstances. I fly helicopters so not sure if that is just a rumour?

W.
#907549 by Blacky1
21 Jul 2015, 20:26
PilotWolf wrote:
mallin wrote:This is in reply to your question from my husband, an ex RAF aircraft engineer.

They are lifted into position using winches and fixed to the wing with great big bolts or pins. These pins are in some cases up to two inches in diameter.... They will not break.


Actually I think the bolts are the weak point designed to allow the engine to break away in certain circumstances. I fly helicopters so not sure if that is just a rumour?

W.


Is it not the position in which they are attached that allows them to flip over the wing to ' safety' ?
Surely the bolts have to be sturdy enough to keep the engine in place at all costs ?
#907562 by tontybear
21 Jul 2015, 23:06
Blacky1 wrote:
PilotWolf wrote:
mallin wrote:This is in reply to your question from my husband, an ex RAF aircraft engineer.

They are lifted into position using winches and fixed to the wing with great big bolts or pins. These pins are in some cases up to two inches in diameter.... They will not break.


Actually I think the bolts are the weak point designed to allow the engine to break away in certain circumstances. I fly helicopters so not sure if that is just a rumour?

W.


Is it not the position in which they are attached that allows them to flip over the wing to ' safety' ?
Surely the bolts have to be sturdy enough to keep the engine in place at all costs ?


There are different forces that affect a wing so the bolts are designed to hold under X forces but to sheer off if Y force is applied (such as a plane hitting the ground) - the forces are different so the bolts can be designed to act in a particular way depending what forces and stress they are put under.

There are some materials that under certain circumstances are stretchy but in others are rigid.

You can drop a glass on a hard kitchen floor and it doesn't smash but if you knock it on the side of the washing up bowl it does.

Also thinking that with a seat belt if you try and yank it the mechanism siezes up but if you pull it gently it doesn't. You want the latter when putting it on or taking it off normally but the former when the car comes to a sudden stop.

I've probably offended every materials scientist in the world now by this explanation !
#907571 by abraxias
22 Jul 2015, 09:06
Yes it does indeed appear that the engines are held in place by three or four bolts 8-) which are strong enough to keep it from falling off, but will let the engine detach if there's impact to avoid further damage to the wing.

I trust the engineers as flying is clearly safe but a marvel for those of us who are rubbish at physics!
#908111 by kushty
03 Aug 2015, 13:58
Also you will have noticed when they spool the engines up to take off power, they do it in two stages, a small amount to get the aircraft moving and then up to take off power to reduce the stress on the engines from a standing start. Also I heard that there aren't many airports in the world that require a 747 to use full power for take off, don't know how true that is.
#908149 by Fuzzy14
04 Aug 2015, 12:57
They may only be held on by three or four bolts but the bolts are operating in shear not tension, which is many times stronger. The bolts are also forged, this means they're squashed when the metal is cooling so that all the material grains face a uniform direction, making it stronger and reduces the risk of cracking.

The strut itself is mostly empty, materials pressed into shapes, especially carbon fibre where you can control the grain direction, is far stronger than a solid lump of metal. Think about a railway bridge made out of triangles instead of a solid lump and you're got the right idea.

Have a look at AAIB's reports especially one that looks at material failure (usually cracks in landing gear) as the pictures give wonderful demonstrations of the materials and structures used in manufacture. The usual joke is the Black Box is indestructible so why don't they make planes out of the same material? Well the primary function of a plane is it needs to fly...

(BEng(hons) AMIMechE)
#908573 by Concorde RIP
14 Aug 2015, 11:51
Just to add a little.

One specific about engine attachment is that they are indeed expressed designed to dettach under the "wrong" circumstances. For example, the plane that ditched in the Hudson, the engines should have dettached so that the weight of the engines was removed thus giving the plane more boyancy and allowing passengers to get off....

A planes engines are rarely, if ever, operated at maximum possible thrust - this would be reduce the life span of the engine and mean more frequent checks.

Another consideration, particularly for the 747, is that it is designed to operate (in fact take off) on only 3 engines, and could fly on 2 provided they are on opposite sides of the plane.

As you can see then, if a plane like that could take off on just 3 engines (a certification requirement), then each engine is capable of far more power than is used under normal circumstances.

There are videos on Youtube of 747's taking off from rediculously short runways due to various circumstances, but of course there will be a minimum runway length - therefore, there will be airports that couldn't take a 747 - but no international ones really (Insbruck could be interesting!!!).

Before take off, calculations are performed based on many, many factors including amount of fuel, weight of cargo/passengers/luggage, temporature, altitude (of the airport) and so on. These all feed in and generate an engine power setting that safely uses a porportion of the runway length to take off - this is mainly to reduce engine stress, but also reduce fuel burn.
#917715 by AlanA
21 Feb 2016, 14:55
There was one if these air crash investigation programmes (love them)
That was a 747 cargo that went down in Holland I think. One of the pins did shear, the engine ripped off and took the plane down....
Virgin Atlantic

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